The best way to pick a fight with a Silastic Armourfiend was just to be born. They didn't like it, they got resentful.
The Guide's view on the Silastic Armourfiends

The Silastic Armourfiends were an insanely aggressive race who lived on the planet Striterax approximately twenty billion years ago "when the universe was young". They were extremely keen on fighting – one of the best ways to deal with a Silastic Armourfiend was to lock him in a room by himself, since he would beat himself up sooner or later. They wrecked the surface of their planet in constant wars, and the whole population lived within bunkers deep below the surface.

In an attempt to deal with the problems their violent nature created, the Silastic Armourfiends passed a law that anybody who had to carry a weapon as part of their normal work (including policemen, security guards and primary school teachers) must spend a minimum of 45 minutes each day punching a sack of potatoes. It was hoped that this would allow them to work off their surplus aggression. This plan worked only until someone had the idea to simply shoot the potatoes, and the Silastic Armourfiends were excited about their "first war for weeks."

During one of their more unpleasant wars, the Silastic Armourfiends asked the great computer Hactar to design the Ultimate Weapon for them. The computer complied, creating a hand-held bomb which would connect the core of every major sun via hyperspace, destroying the entire universe. The Silastic Armourfiends attempted to use the bomb to blow up a munitions dump, but fortunately Hactar had built a dud weapon since it could not conceive of any occasion when the use of the real thing would be justified. The Silastic Armourfiends disagreed, and pulverised Hactar.

Eventually, after smashing the hell out of the Strenuous Garfighters of Stug and the Strangulous Stilettians of Jajazikstak, the Silastic Armourfiends found an entirely new way of blowing themselves up, which was of great relief to the Garfighters, the Stilletans, and the potatoes.